In a hydraulic control system for an excavator or other work machine, a pump delivery amount increases in accordance with the operation amount of an operating device, and at the same time, a spool in a control valve is operated by a pilot pressure based on the operation amount to permit a hydraulic pump to communicate with hydraulic actuators such as a hydraulic cylinder and a hydraulic motor. As the spool in the control valve has an opening formed to vary in accordance with a stroke, the degree of communication between the hydraulic actuators and the hydraulic pump can be changed by the pilot pressure.
Consequently, when a combined operation is performed to simultaneously operate a plurality of hydraulic actuators, the pump delivery amount can be divided to operate in combination the hydraulic actuators in accordance with the operation amounts of individual operating devices.
A hydraulic control circuit for a construction machine that is described, for instance, in Patent Document 1 controls a first pump and a second pump in order to avoid a decrease in an operating speed when a hydraulic actuator for an attachment and another hydraulic actuator operate in combination with each other. The hydraulic control circuit is capable of supplying hydraulic fluid from the first pump to the hydraulic actuator for the attachment and another hydraulic actuator through an associated spool and from the second pump to the hydraulic actuator for the attachment and another hydraulic actuator through an associated spool. The first pump and the second pump are controlled in such a manner that the flow rate obtained when the hydraulic actuator for the attachment and another hydraulic actuator operate in combination with each other is equal to the sum of the flow rate of the hydraulic actuator for an attachment and the flow rate of the other hydraulic actuator.